Method of crushing



G. JOHNSTON.

METHOD OF CHUSHING. APPLICATION FILED AUG.27, 1921.

Patented Nov. 8, 1921.

UNITED STATES GEORGE JOHNSTON, 0F MANCHESTER, ENGLAND.

METHOD OF GRUSHING.

Specification of Letters Patent.

Patented Nov. 8, 1921.

Application filed August 27, 1921. Serial No. 495,976.

To all whom it may concern:

Be it known that I, GEORGE JOHNSTON, a subject of the King of Great Britain and Ireland, residing at Manchester, England, have inventedcertain new and useful Improvements in Methods of Crushing, for which I have filed British patent applica tion No. 22,672, dated July 30, 1920, of which the following is a specification.

My invention relates to the art of crushing and particularly to an improved method of crusher operation by which reatly increased output may be secured with greatly diminished wear upon the apparatus andat a much lower power consumption and initial.

plant expense.

The method is particularly applicable to the reduction of coarse material such as ore broken to the size of a pea or smaller, to a pulverulent condition, such as would pass for instance, a two hundred mesh screen. If the material is a precious metal ore, such as gold quartz, for example, the values may be extracted very com letely and rapidly from such fines. While t e method is particularly applicable for the treatment of such ores, its utility is by no means confined to this field and the method may be applied to the com.- minution of any-suitable materials such as cement, coal, etc., particularly hard or gritty materials as are apt to have a serious abrasive action on the crusher rolls. Preterably, the material is treated in a dry condition, but it may be moist to such an extent as will not interfere with the method of operation set forth.

- The customary method of operating crushers, or crushers of the type to which the present invention relates, is to choke feed the roll pairs from a hopper or conve er. The discharge from the first pair 0 rolls is passed through successive roll pairs by grav- 1ty or by conveyers without any attempt to break up the sheeted or caked material between successive passes. low efficiency, and necessitates the use of very heavy and powerful rolls with incidental heavy power demand, since the caked material strongly resists further crushing. Moreover, the choke feed to the rolls causes a severe abrasive action thereon, which ma- ,terially shortens their period of utility and service. In order to minimize the abrasive effect, the rolls are commonly rotated at relatively slow speed.

The underlying thou hts of the present invention are, first, to rive the rolls at a This results in a high speed, say at a peripheral speed of two thousand to fifteen thousand feet per minute, second, feed the material to the rolls, at substantially their peripheral speed so as to eliminate abrasive action so far as possible, third, to break up the caked or sheeted material discharged from one roll pair before it reaches the succeeding pair so that the particles are separated and individually pre sented to the rolls of each pair, and, fourth, to employ an air current induced by suction for propelling the material through the apparatus, not only to secure a proper feed velocity for the material, but also to assist in breaking up the cakes or sheets between successive passes. The induced air current has the marked advantage over forced blast, that the bearings are kept free from dust, and the flow of air through the apparatus is kept even and smooth Without back pressure which might tend to disturb the flow of the material to the rolls. 1 amaware that in certain coal breakers it has been suggested to drop the large coal lumps by gravity to the breaker rolls with the idea of attaining a feed speed substantially the same as the peripheral speed of the breaker rolls. Such a practice would be totally impossible when dealing with high speed rolls and with moreor less pulverulent materials.

Inasmuch as any crushing operation necessitates the use of appropriate apparatus, I refer to that diagrammatically illustrated on the accompanying sheet of drawings for the purpose of explaining the invention,

which is related to that of my copending application Ser. No. 492,458, filed August 15, 1921.

While the invention may be carried out in apparatus of various types of constructlon, that indicated comprises two pairs of crushing rolls, the to pair A B receiving the coarse material from the hopper D, while the second pair from the first pair and delivers it to channels leading to the suction fan Between the hopper and the rolls is an air feed duct H, divided by a guide plate or' fin I, the lower edge of which projects beyond the lower margin of the feed duct H and approaches the nip of the rolls A B.

An air by-pass K around each roll leads to a second feed duct L similarly divided by a fin M terminating adjacent the nip of the E F receives the discharge rolls E F. Beneath the rolls A B is a divert- I ing rolls impinges and is not only broken up but diverted in opposite directions so that it fallson opposite sides of the spreader O.

Passing down these sides the stream of partially crushed material meets the air flowing in the by-pass K, at an angle and the adhesion between the particles of the caked rated and the cakes or sheets which resist further crushing action have been eliminated so far as possible. This is a very important ste in the method, since the action of the rol s E F upon the material rendered muchv more effective than would be the case were the material to pass from the rolls A B to the rolls E F without a thorough separation of the particles of the partially crushed material. The effectiveness of the rolls E F is so greatly increased that at a relatively low ressure the maximum crushing effect by t e rolls is secured,

and the rolls may therefore be made much A B lighter than usual while less power is required to drive them. I

A secondary by-pass K around the rolls communicates with the discharge passage L from the latter and leads either to further crushing rolls or to the suction fan G.

l The value of the air current as an aid to the breaking up of abrasive action between the particles of caked material has been pointed out above. Its associated function isto propel and deliver the material to the rolls at a speed substantially corresponding to their peripheral speed in order to prevent abrasive action thereon. It will be noted that the feed ducts H and L are constricted at their delivery ends and fairly .closely approach the guide fins l and M. be velocity of the air current is greatest at this point and it may be regulated in accordance with the characteristics of the material at each pass and with the speed of the rolls at each pass, as well as with relation to the capacity of the fan G. The material 1s thus fed to the rolls at substantially their peripheral speed and the abrasive action which occurs when the material meets the rolls either faster or slower than their peripheral speed, or when there is a choke feed, is substantially eliminated. The life of the rolls is thus greatly lengthened.

It may. be pointed out that in order to handle at the rolls E F a volume of material commensurate to that passing the pair s thereby of rolls A B which are placed sli htly farther apart, it may be necessary to drive the rolls E F at a slightly greater speed. Alternatively, if the rolls are all rotated at substantially the same speed, the feed of the material to the first roll pair is so regulated with respect to the capacity of the final roll pair that there is no piling up of the partially comminuted material at any of the roll passes. It may be pointed out, how ever, that as the material progresses through the roll series a portion of its volume is suliiciently comminuted at each pass to be taken up by the air current and carried around with it in the by-pass channels, so that as a matter of fact the volume of the material entering the final roll pair may be materially less than that entering the first roll pair.

It will be noted that the by-pass channels are not of uniform cross sectional area at all points; thus the relatively quiet chamber P adjacent the inlet duct H minimizes the lateral escape draft, which otherwise might tend to disturb the feed of the material to the .nip of the rolls. The chamber R below the rolls A B forms an eddy or whirlpool chamber in which the disturbed air currents assist in breaking up the adhesions between the particles of material caked by the crushing action of the rolls The method of operation set forth and the advantages derived therefrom are not dependent upon a particular construction of apparatus and while I have claimed the particular construction indicated in my copending application above referred to, the invention is not thus limited, but embodies what I claim as broader principles of operation.

I claim 1. In the art of crushing, the step of driving a pair ofcrushing rolls at a peripheral speed of at least two thousand feet per minute and propelling material to said rolls at a speed substantially corresponding thereto.

2. In the art of crushing by means of high speed rolls, the method of feeding material to the rolls by propelling said material by an air current having a velocity such as to deliver the material to the rolls at a speed substantially corresponding to the peripheral speed of the rolls.

3. In the art of crushing by means of high speed rolls, the method of feeding material to the rolls by propelling, said material by an air current having a velocity such as to deliver the material to the rolls at a speed substantially corresponding to the Jeripheral speed of the rolls, and guiding t e material substantially to the nip of the rolls.

4. In the art of crushing by passing material through successive pairs of crushing rolls, the method of feeding the material to the rolls which consists in propelling the material in a current of air to the first pair of rolls, by-passing the major portion of the air current around said first pair of rolls and delivering the partially crushed mate rial thereto and guiding said propelling air current to the second pair of rolls to deliver the partially crushed material thereto.

5. In the art of crushing by passing material through successive pairs of crushing rolls, the method of feeding material from one roll pair to the succeeding roll pair, which consists in leading a current of air to the second pair of rolls and guiding into the air current at an angle to its direction of flow the partially crushed material of the preceding pair of crushing rolls whereby the adhering particles of material are separated by the impingement of the air current thereagainst and are propelled thereby to said second roll pair.

6. In the art of crushing by passing material through successive airs of crushing rolls, the method of feeding material from one roll pair to the succeeding roll pair which consists in delivering the partially crushed material from one roll pair to an air current and propelling the material by said air current against a surface to brea up the adhesion between the particles of said partially crushed material and then leading the separated particles to the succeeding roll pair.

7 In the art of crushing by passing material through successive pairs of crushing rolls, the method of breaking up adhesion between the particles of the partially crushed material delivered by one pair of rolls which consists in causing said material to impinge against a surface adapted to break up the adhesion between particles thereof, and then propelling said particles by means of a current of air to the nip of a succeeding roll pair.

8. In the art of crushing by passing material through successive pairs of crushing rolls, the method of breaking up adhesion between particles of the partially crushed material delivered by one pair of rolls which consists in causing said material to impinge against a surface adapted to break up the adhesion between particles thereof, and then propelling. said particles by means of a current of air against a surface to further break up the adhesion of said particles and leading the material to the nip of a succeeding roll pair.

9. In the art of crushing by passing material through successive pairs' of crushing rolls, the method of breaking up adhesion between particles of the partially; crushed.

rolls,

ma terial delivered by one pair to which consists in causing said delivered material against a surface ada the adhesion between particles thereof and discharging the material from said surface into a current of air flowing at an angle thereto and leading to the succeeding roll pa r.

10. In the art of crushing by passing material through successive pairs of crushing rolls rotated at high speed, he method of feeding material thereto which consists in propelling the same in an air current to the first roll pair, at a speed substantially corresponding to the peripheral speed of said rolls, by-passing said air current around pted to break up said first roll pair and leading it to the succeeding roll pair, delivering to said bypassed air current the partially crushed material discharged from the first roll pair and causing the adhesion between particles of material to be broken up during its travel between said roll airs.

In testimony w ereof I hereunto aflix my signature.

G. JOHNSTON. 

